Add regression test for matches! + non_exhaustive_omitted_patterns lint

Author: jplatte

coretests/tests/lib.rs

@@ -76,6 +76,7 @@
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(next_index)]
+#![feature(non_exhaustive_omitted_patterns_lint)]
 #![feature(numfmt)]
 #![feature(pattern)]
 #![feature(pointer_is_aligned_to)]

coretests/tests/macros.rs

@@ -213,3 +213,9 @@ fn _expression() {
         }
     );
 }
+
+#[deny(non_exhaustive_omitted_patterns)]
+fn _matches_does_not_trigger_non_exhaustive_omitted_patterns_lint(o: core::sync::atomic::Ordering) {
+    // Ordering is a #[non_exhaustive] enum from a separate crate
+    let _m = matches!(o, core::sync::atomic::Ordering::Relaxed);
+}